When saving an email message to a network drive, I get the following error;

“The message interface has returned an unknown error.”

Instead of saving the message, a tmp-file is created on the network location. When I rename the tmp-file to .msg, then it appears to be the message that I tried to save.

How can I get rid of the error and have the message save directly as an msg-file?

This issue appears to be specific to running Outlook 2007 or Outlook 2010 on Windows Vista or Windows 7. It also appears to happen more often to network shares that are either part of a Distributed File System (DFS) structure or located on storage hardware which isn’t running on Windows like a dedicated NAS system.

The solution is to disable a feature called “Robustified UNC” via the Registry;

While the registry key is located in the Word hive, it actually applies to Outlook (and other Office applications) as well. Due to its location, it could be required to close all open Office applications before changes to take affect (or simply restart your computer).

Robustified UNC

While the effect of the registry key has not been publicly documented by Microsoft, the “Robustified UNC” feature affects the security mechanisms used when opening a file from or saving a file to a network share in Office applications.

Disabling the “Robustified UNC” feature could also solve issues such as documents not opening when double clicked from a network share (while Word does open) or hangs or slow performance when opening/saving files that are located on a network share.

If you are using Outlook 2007, make sure you’ve applied all updates before trying to implement this registry key as the option to turn it off might have been added by a Service Pack or update.

If changing this registry key does not solve your immediate issue, it is recommended to remove it again.

If the registry change does solve your issue, it is still recommended to remove the key and test Outlook’s behavior whenever you install an Office update as the “Robustified UNC” feature might get a fix (Microsoft is aware of the issue).

In any case, use the registry change with caution until the full effect of the key has been published by Microsoft so you can understand the risk in full.

Note: This post is based on a forum discussion which can be found here.